Muscle hypertrophy - AbsoluteAstronomy.com

Muscle hypertrophy is an increase in the size of muscle

Muscle

Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

cells. It differs from muscle hyperplasia

Hyperplasia

Hyperplasia means increase in number of cells/proliferation of cells. It may result in the gross enlargement of an organ and the term is sometimes mixed with benign neoplasia/ benign tumor....

, which is the formation of new muscle cells.

Hypertrophy stimuli

A range of stimuli can increase the volume of muscle cells. Summarizing, these changes occur as an adaptive response that serves to increase the ability to generate force or resist fatigue in anaerobic conditions.

Strength training

Strength training is the use of resistance to muscular contraction to build the strength, anaerobic endurance, and size of skeletal muscles. There are many different methods of strength training, the most common being the use of gravity or elastic/hydraulic forces to oppose muscle contraction...

typically produces a combination of the two different types of hypertrophy: contraction against 80 to 90% of the one repetition maximum

One rep maximum

One rep maximum in weight training is the maximum amount of weight one can lift in a single repetition for a given exercise. One repetition maximum can be used for determining an individual's maximum strength and is the method for determining the winner in events such as powerlifting and...

for 2–6 repetitions (reps) causes myofibril

Myofibril

A myofibril is a basic unit of a muscle. Muscles are composed of tubular cells called myocytes or myofibers. Myofibers are composed of tubular myofibrils. Myofibrils are composed of long proteins such as actin, myosin, and titin, and other proteins that hold them together...

lated hypertrophy to dominate (as in powerlifters

Powerlifting

Powerlifting is a strength sport. It resembles the sport of Olympic weightlifting, as both disciplines involve lifting weights in three attempts. Powerlifting evolved from a sport known as 'odd lifts' which followed the same three attempt format but used a wide variety of events akin to Strongman...

, olympic lifters and strength athletes), while several repetitions (generally 8 – 12 for bodybuilding or 12 or more for muscular endurance) against a sub-maximal load facilitates mainly sarcoplasm

Sarcoplasm

The Sarcoplasm of a muscle fiber is comparable to the cytoplasm of other cells, but it houses unusually large amounts of glycosomes and significant amounts of myoglobin, an oxygen binding protein...

ic hypertrophy (professional bodybuilders

Bodybuilding

Bodybuilding is a form of body modification involving intensive muscle hypertrophy. An individual who engages in this activity is referred to as a bodybuilder. In competitive and professional bodybuilding, bodybuilders display their physiques to a panel of judges, who assign points based on their...

and endurance athletes). The first measurable effect is an increase in the neural drive stimulating muscle contraction. Within just a few days, an untrained individual can achieve measurable strength gains resulting from "learning" to use the muscle. As the muscle continues to receive increased demands, the synthetic machinery is upregulated. Although all the steps are not yet clear, this upregulation appears to begin with the ubiquitous second messenger system (including phospholipase

Phospholipase

A phospholipase is an enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances. There are four major classes, termed A, B, C and D, distinguished by the type of reaction which they catalyze:*Phospholipase A...

s, protein kinase C

Protein kinase C

Protein kinase C also known as PKC is a family of enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and threonine amino acid residues on these proteins. PKC enzymes in turn are activated by signals such as increases in...

, tyrosine kinase

Tyrosine kinase

A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to a protein in a cell. It functions as an "on" or "off" switch in many cellular functions....

, and others). These, in turn, activate the family of immediate-early genes, including c-fos, c-jun and myc. These genes appear to dictate the contractile protein gene response.

To get the best gains out of training sessions, experts agree on some basic principles, however, some are contradicted by other research:

Progressive overload

Progressive overload

Progressive overload is the gradual increase of stress placed upon the body during exercise training. It was developed by Thomas Delorme, M.D. while he rehabilitated soldiers after World War II...

is considered the most important principle behind hypertrophy, so increasing the weight, repetitions (reps), and sets will all have a positive impact on growth. Some experts create complicated plans that manipulate weight, reps, and sets, increasing one while decreasing the others to keep the schedule varied and less repetitive. It is generally believed that if more than 15 repetitions per set is possible, the weight is too light to stimulate maximal growth.

Anaerobic training

Experts and professionals differ widely on the best approaches to specifically achieve muscle growth (as opposed to focusing on gaining strength, power, or endurance); it was generally considered that consistent anaerobic strength training will produce hypertrophy over the long term, in addition to its effects on muscular strength and endurance. As testosterone

Testosterone

Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...

is one of the body's major growth hormones, on average, men find hypertrophy much easier to achieve than women. Taking additional testosterone, as in anabolic steroid

Anabolic steroid

Anabolic steroids, technically known as anabolic-androgen steroids or colloquially simply as "steroids", are drugs that mimic the effects of testosterone and dihydrotestosterone in the body. They increase protein synthesis within cells, which results in the buildup of cellular tissue ,...

s, will increase results. It is also considered a performance-enhancing drug

Doping (sport)

The use of performance-enhancing drugs in sport is commonly referred to by the term "doping", particularly by those organizations that regulate competitions. The use of performance enhancing drugs is mostly done to improve athletic performance. This is why many sports ban the use of performance...

, the use of which can cause competitors to be suspended or banned from competitions. In addition, testosterone is also a medically regulated substance in most countries, making it illegal to possess it without a medical prescription

Medical prescription

A prescription is a health-care program implemented by a physician or other medical practitioner in the form of instructions that govern the plan of care for an individual patient. Prescriptions may include orders to be performed by a patient, caretaker, nurse, pharmacist or other therapist....

Factors affecting hypertrophy

Several biological factors such as age and nutrition can affect muscle hypertrophy. During puberty in males, hypertrophy occurs at an increased rate. Natural hypertrophy normally stops at full growth in the late teens. Muscular hypertrophy can be increased through strength training

Strength training

and other short duration, high intensity anaerobic exercises. Lower intensity, longer duration aerobic exercise

Aerobic exercise

Aerobic exercise is physical exercise of relatively low intensity that depends primarily on the aerobic energy-generating process. Aerobic literally means "living in air", and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism...

generally does not result in very effective tissue hypertrophy; instead, endurance athletes enhance storage of fats and carbohydrates

Glycogen

Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...

within the muscles, as well as neovascularization

Neovascularization

Neovascularization is the formation of functional microvascular networks with red blood cell perfusion. Neovascularization differs from angiogenesis in that angiogenesis is mainly characterized by the protrusion and outgrowth of capillary buds and sprouts from pre-existing blood vessels.In...

. An adequate supply of amino acids is essential to produce muscle hypertrophy.

Protein synthesis

Ultimately the message filters down to alter the pattern of protein expression

Protein expression

Protein expression is a subcomponent of gene expression. It consists of the stages after DNA has been translated into polypeptide chains, which are ultimately folded into proteins...

. The additional contractile proteins appear to be incorporated into existing myofibrils (the chains of sarcomere

Sarcomere

A sarcomere is the basic unit of a muscle. Muscles are composed of tubular muscle cells . Muscle cells are composed of tubular myofibrils. Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as dark and light bands...

s within a muscle cell). There appears to be some limit to how large a myofibril can become: at some point, they split. These events appear to occur within each muscle fiber. That is, hypertrophy results primarily from the growth of each muscle cell, rather than an increase in the number of cells. Skeletal muscle

Skeletal muscle

Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...

cells are however unique in the body in that they can contain multiple nuclei, and the number of nuclei can increase.

Cortisol

Cortisol

Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...

decreases amino acid uptake by muscle tissue, and inhibits protein synthesis. The short-term increase in protein synthesis that occurs subsequent to resistance training returns to normal after approximately 28 hours in adequately fed male youths.

A small study performed on young and elderly found that ingestion of 340 grams of lean beef

Beef

Beef is the culinary name for meat from bovines, especially domestic cattle. Beef can be harvested from cows, bulls, heifers or steers. It is one of the principal meats used in the cuisine of the Middle East , Australia, Argentina, Brazil, Europe and the United States, and is also important in...

(90 g protein) did not increase muscle protein synthesis any more than ingestion of 113 grams of lean beef

Beef

(30 g protein). In both groups, muscle protein synthesis increased by 50%. The study concluded that more than 30 g protein in a single meal did not further enhance the stimulation of muscle protein synthesis in young and elderly. However, this study didn't check protein synthesis in relation to training; therefore conclusions from this research are controversial.

It is not uncommon for bodybuilders to advise a protein intake as high as 2–4 g per kilogram of bodyweight per day. However, scientific literature such as 'Evaluation of protein requirements for trained strength athletes (November 1992)' has suggested this is higher than necessary, as protein intakes greater than 1.8 g per kilogram of body weight showed to have no greater effect on muscle hypertrophy. A study carried out by American College of Sports Medicine (2002) put the recommended daily protein intake for athletes at 1.2–1.8 g per kilogram of body weight. Conversely, Di Pasquale

Mauro Di Pasquale

Mauro G. Di Pasquale, B.Sc., MD, MRO, MFS is a bodybuilding author and columnist. Di Pasquale was an assistant professor at the University of Toronto from 1988 to 1998. He lectured and researched on athletic performance, nutritional supplements and drug use in sports...

(2008), citing recent studies, recommends a minimum protein intake of 2.2 g/kg "for anyone involved in competitive or intense recreational sports who wants to maximize lean body mass but does not wish to gain weight. However athletes involved in strength events (..) may need even more to maximize body composition and athletic performance. In those attempting to minimize body fat and thus maximize body composition, for example in sports with weight classes and in bodybuilding, it’s possible that protein may well make up over 50% of their daily caloric intake.

Microtrauma

Microtrauma is the general term given to small injuries to the body.Microtrauma can include the microtearing of muscle fibres, the sheath around the muscle and the connective tissue. It can also include stress to the tendons, and to the bones . It is unknown whether or not the ligaments adapt like...

, which is tiny damage to the fibers, may play a significant role in hypertrophy. When microtrauma occurs (from weight training or other strenuous activities), the body responds by overcompensating, replacing the damaged tissue and adding more, so that the risk of repeat damage is reduced. Damage to these fibers have been theorized as the possible cause for the symptoms of delayed onset muscle soreness

Delayed onset muscle soreness

Delayed onset muscle soreness , also called muscle fever, is the pain and stiffness felt in muscles several hours to days after unaccustomed or strenuous exercise. The soreness is felt most strongly 24 to 72 hours after the exercise. It is caused by eccentric exercise...

(DOMS), and is why progressive overload is essential to continued improvement, as the body adapts and becomes more resistant to stress.

Myofibrillar vs. Sarcoplasmic hypertrophy controversy

In the bodybuilding and fitness community and even in some academic books skeletal muscle hypertrophy is described as being in one of two types: Sarcoplasmic or myofibrillar. According to this theory, during sarcoplasmic hypertrophy, the volume of sarcoplasm

Sarcoplasm

The Sarcoplasm of a muscle fiber is comparable to the cytoplasm of other cells, but it houses unusually large amounts of glycosomes and significant amounts of myoglobin, an oxygen binding protein...

ic fluid in the muscle cell increases with no accompanying increase in muscular strength, whereas during myofibrillar hypertrophy, actin

Actin

Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...

and myosin

Myosin

Myosins comprise a family of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility processes. They are responsible for actin-based motility. The term was originally used to describe a group of similar...

contractile proteins increase in number and add to muscular strength as well as a small increase in the size of the muscle. Sarcoplasmic hypertrophy is characteristic of the muscles of certain bodybuilders while myofibrillar hypertrophy is characteristic of Olympic weightlifters. These two forms of adaptations rarely occur completely independently of one another, one can experience a large increase in fluid with a slight increase in proteins, a large increase in proteins with a small increase in fluid, or a relatively balanced combination of the two.
In contrast to this theory it should be noted that when viewed in microscope, muscles are filled entirely by myofibrils, whether or not the muscles from bodybuilders or powerlifters are used. Also, very little actual evidence actually supports that the non-myofibrillar part of the sarcoplasm ever expands. Antagonists to this theory suggest that the cause of this popular notion is twofold: First, it is derived from fractioning of muscle used when measuring protein synthesis. This is a technique in which muscle proteins are separated biochemically into myofibrillar, sarcoplasmic, membrane and mitochondrial fractions for protein synthesis. This validity of this separation is poorly validated and also, the results of this fractionation and the usual following stable isotope protein synthesis measurement does not tell anything about the relative abundance of these protein fractions (as changes in protein synthesis are by definition relative (i.e. a change of 50% in a substance that constitutes 1% of the muscle is still insignificant in a physiological context). Secondly, the sarcoplasmic/myofibrillar proponents use their theory to explain why bodybuilders have less relative strength than strength athletes. But this theory is not necessary to explain these differences. The physiological changes associated with training with very high volume and degrees of muscle fatigue produce difference neuromuscular adaptations that are different from those experienced by strength training with very high mechanical loads and less muscle fatigue.

In sports

Examples of increased muscle hypertrophy are seen in various professional sports, mainly strength related sports such as boxing

Boxing

Boxing, also called pugilism, is a combat sport in which two people fight each other using their fists. Boxing is supervised by a referee over a series of between one to three minute intervals called rounds...

, bodybuilding

Bodybuilding

, mixed martial arts

Mixed martial arts

Mixed Martial Arts is a full contact combat sport that allows the use of both striking and grappling techniques, both standing and on the ground, including boxing, wrestling, Brazilian jiu-jitsu, muay Thai, kickboxing, karate, judo and other styles. The roots of modern mixed martial arts can be...

, rugby

Rugby football

Rugby football is a style of football named after Rugby School in the United Kingdom. It is seen most prominently in two current sports, rugby league and rugby union.-History:...

, professional wrestling

Professional wrestling

Professional wrestling is a mode of spectacle, combining athletics and theatrical performance.Roland Barthes, "The World of Wrestling", Mythologies, 1957 It takes the form of events, held by touring companies, which mimic a title match combat sport...

and various forms of gymnastics

Gymnastics

Gymnastics is a sport involving performance of exercises requiring physical strength, flexibility, agility, coordination, and balance. Internationally, all of the gymnastic sports are governed by the Fédération Internationale de Gymnastique with each country having its own national governing body...

. These athletes train extensively in strength

Strength training

as well as cardiovascular and muscular endurance training.

Hypertrophy stimuli

Strength training

Anaerobic training

Factors affecting hypertrophy

Protein synthesis

Microtrauma

Myofibrillar vs. Sarcoplasmic hypertrophy controversy

In sports

See also